1. Field of the Invention
The present invention relates to an exhaust apparatus for a vehicle and a motorcycle having the exhaust apparatus.
2. Description of the Related Art
In an exhaust apparatus for a vehicle, an exhaust path from an exhaust port of an engine to an inlet of an exhaust muffler is constituted by an exhaust path forming member such as an exhaust pipe or the like. Typically, the exhaust path is composed of a plurality of exhaust path forming members connected to each other as a matter of convenience for a layout of the exhaust apparatus, a length of the exhaust path or an installation of a catalyst apparatus.
In the case of connecting the exhaust path forming members made of the same material to each other, for example, in the case of connecting the exhaust path forming members made of stainless steel to each other, or in the case of connecting the exhaust path forming members made of titanium to each other, it is possible to join them by welding with a compact configuration and high sealing performance.
On the other hand, in the case of connecting the exhaust path forming members made of the different materials to each other, it is hard to join them by welding. Accordingly, they have been conventionally connected by a fitting joint using a clamp. In other words, in FIG. 11, end portions 301a and 302a of exhaust path forming members 301 and 302 made of the different materials are fitted to each other via a seal 305, and an outer peripheral surface of the fitted portions is fastened by an annular clamp 303. See for example, the Japanese Unexamined Utility Model Publication No. H02-101014.
Further, in the conventional exhaust apparatus for the motorcycle, there is often the case that the catalyst apparatus is installed in the exhaust muffler arranged in a rear portion of a vehicle body, as disclosed in Japanese Patent No. 3022358.
In this case, since the length of the exhaust path from the exhaust port of the engine to the catalyst apparatus becomes long, and an exhaust gas is brought into contact with the catalyst apparatus in a state in which the temperature of the exhaust gas is lowered, and activation of the catalyst apparatus is lowered.
Conversely, if the catalyst apparatus is arranged in the exhaust path forming member in the front of the engine, it is possible to make the length of the exhaust path from the exhaust port to the catalyst apparatus short. In this case, since a radiator or the like is arranged in the front of the engine, the layout space for the catalyst apparatus is limited, and a temperature of the catalyst apparatus is lowered due to a direct application of running wind on traveling or wind from the radiator.
Further, as disclosed in Japanese Unexamined Patent Publication No. H06-26375, there is an exhaust apparatus in which the catalyst apparatus is arranged under the engine. As shown in FIG. 12, an exhaust pipe 405 of the exhaust apparatus made of titanium has an expanded portion 405a under an engine 410. The catalyst apparatus 400 is made of stainless steel, and is composed of a cylindrical case 402 and a metal honeycomb 401 built the cylindrical case 402. The catalyst apparatus 400 is arranged within the expanded portion 405a, and the cylindrical case 402 is fixed to the expanded portion 405a via a bracket 411. The bracket 411 is made of titanium, and is fixed to the expanded portion 405a made of the same material by welding. In the case, the bracket 411 is coupled to the cylindrical case 402 made of the different material by caulking or bending.
3. Problems to be Solved by the Invention
Returning now to FIG. 11, it is necessary to form linear fitting portions 301a and 302a in the respective exhaust path forming members 301 and 302. However, the linear fitting portions 301a and 302a have a fixed length L1 in a length direction of an exhaust path. Accordingly, a dimension of the connecting portion (the fitting portions 301a and 302a) in the length direction of the exhaust path is increased, and a wide work space more than the length L1 is required at a connecting work (at an assembling work). Whereby, it becomes hard to execute the connecting work in the narrow space. Further, a pair of protruding pieces 307 for contracting the annular clamp 303 are formed in the annular clamp 303 so as to protrude outward in a radial direction. The protruding pieces 307 are provided with a nut 311 and a bolt 310 inserted to the protruding pieces 307. The annular clamp 303 is fastened on an outer peripheral surface of the fitting portion 302a by contracting by the bolt 310 and the nut 311. Accordingly, a wide layout space is necessary in a radial direction.
Particularly, in the case that it is necessary to arrange the exhaust path forming member compactly around the engine such as the motorcycle, it is hard to compactly arrange the exhaust apparatus by utilizing only the fitting joint using the clamp 303.
Further returning to FIG. 12, since the expanded portion 405a accommodating the catalyst apparatus 400 is made of the titanium, and the catalyst apparatus 400 is made of the stainless steel, it is impossible to join the catalyst apparatus 400 to the expanded portion 305a made of the different material by welding. Accordingly, the bracket 411 is interposed between the expanded portion 405a and the case 402, and the bracket 411 mechanically holds the case 402 by caulking or bending, and is fixed to the expanded portion 405a by welding.
If the bracket 411 as shown in FIG. 12 is provided, a number of parts for assembling the catalyst apparatus 400 is increased, and two assembling processes comprising a caulking process and a welding process are necessary when the catalyst 400 is installed in the expanded portion 405a. Further, since an extra annular space for arranging the bracket 411 is required between the expanded portion 305a and the case 402, a diameter of the expanded portion 405a is enlarged so as to sufficiently secure an exhaust gas distributing cross sectional area of the catalyst apparatus 400. In this case, particularly in the motorcycle, if the outer diameter of the expanded portion 305a arranged under the engine 410 is enlarged, a bank angle and a minimum road clearance of the motorcycle may become small.